1. Field of the Invention
The present invention relates to fuel cell assemblies comprising one or more microfibrous fuel cell elements containing fiber-supported electrocatalyst layers, and methods of making same.
2. Description of the Related Art
The recently developed microfibrous electrochemical cells, as disclosed by Ray R. Eshraghi in U.S. Pat. Nos. 5,916,514; 5,928,808; 5,989,300; 6,004,691; 6,338,913; 6,399,232; 6,403,248; 6,403,517; 6,444,339; and 6,495,281, are advantageously characterized by reduced sizes (outer diameters usually within the range of from about 10 microns to about 10 millimeters) and increased active surface areas, which have demonstrated increased volumetric power density (i.e., unit volume power output) in comparison with conventional flat sheet or flat panel electrochemical cells. Further, such microfibrous electrochemical cells can be easily packed and assembled together. Therefore, by assembling multiple serially-connected and/or parallelly-connected microfibrous cells into a compact multi-cell unit, one can effectively modulate the voltage and/or current output of such multi-cell unit according to specific system requirements. The microfibrous electrochemical cells disclosed by the above-listed U.S. patents thus represent an important advancement in the field of power generation.
Among various microfibrous electrochemical cells, microfibrous fuel cells offer especially attractive features as energy conversion devices, including high energy efficiency and low level gaseous/solid emission, in comparison with traditional combustion-based energy sources. There are therefore particular interests in developing high quality power sources for use in hand-held or mobile electrical devices, electrically powered vehicles, as well as in distributed power generation applications, based on such microfibrous fuel cells.
A generalized microfibrous fuel cell, as described in the above-listed Eshraghi patents, comprises an inner current collector, an inner electrocatalyst layer, a microfibrous hollow membrane separator, an outer electrocatalyst layer, and an outer current collector. Additional components, such as humidifying tubes, heat-exchanging tubes and additional membrane layers, can be further configured and incorporated into the microfibrous fuel cell to improve the cell performance.
The inner and outer electrocatalyst layers of such microfibrous fuel cells are formed of electrocatalyst particles, which are coated onto or impregnated into the inner and outer surfaces of the hollow fibrous membrane separator. Although the catalyst/membrane bond is strong, the membrane-electrode assembly (MEA) may expand and contract during cyclic operation of the fuel cell. This is due to the fact that the ion-exchange polymer membranes used in fuel cells swell or shrink depending on the state of the membrane hydration. The expansion and contraction of the membrane may have a deleterious effect on the MEA structure and long-term performance of the fuel cell.
It is therefore an object of the present invention to provide an improved microfibrous fuel cell element, which comprises electrocatalytical structures characterized by high mechanical strength and robustness that provide good adhesion to the membrane separator even in consideration of the dimensional changes of such membrane separator during operation.
It is another object of the present invention to provide improved microfibrous fuel cells that can be manufactured by continuous extrusion on an automated production line, which enables commercial production of such microfibrous fuel cells, enhancing cell uniformity and consistency, and reducing the associated manufacturing costs.
It is a further object of the present invention to provide a fuel cell assembly comprising multiple improved microfibrous fuel cells connected in series and/or parallel for reliable and consistent power generation.
Other objects of the present invention will be more fully apparent from the ensuing disclosure and appended claims.